/*
 *  linux/fs/ext2/inode.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Goal-directed block allocation by Stephen Tweedie
 * 	(sct@dcs.ed.ac.uk), 1993, 1998
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 1995
 *  64-bit file support on 64-bit platforms by Jakub Jelinek
 * 	(jj@sunsite.ms.mff.cuni.cz)
 *
 *  Assorted race fixes, rewrite of ext2_get_block() by Al Viro, 2000
 */

#include <linux/smp_lock.h>
#include <linux/time.h>
#include <linux/highuid.h>
#include <linux/pagemap.h>
#include <linux/quotaops.h>
#include <linux/module.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h>
#include <linux/mpage.h>
#include <linux/fiemap.h>
#include <linux/namei.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/bio.h>
#include <linux/bit_spinlock.h>
#include <linux/kernel.h>
#include "ext2.h"
#include "acl.h"
#include "xip.h"

MODULE_AUTHOR("Remy Card and others");
MODULE_DESCRIPTION("Second Extended Filesystem");
MODULE_LICENSE("GPL");


int ext2_block_read_full_page(struct page *page, get_block_t *get_block);
static void ext2_end_buffer_async_read(struct buffer_head *bh, int uptodate);
int ext2_compute_checksum(char*, int);
int ext2_read_checksum(struct inode *inode, sector_t iblock);
static struct bio* ext2_mpage_bio_submit(int rw, struct bio *bio);
int
ext2_mpage_readpages(struct address_space *mapping, struct list_head *pages,
		unsigned nr_pages, get_block_t get_block);
static void ext2_mpage_end_io_read(struct bio *bio, int err);
static void ext2_mpage_end_io_write(struct bio *bio, int err);
static int ext2_mpage_readpage(struct page *page, get_block_t get_block);
static struct bio *
ext2_do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
		sector_t *last_block_in_bio, struct buffer_head* map_bh,
		unsigned long *first_logical_block, get_block_t get_block);
static void ext2_mark_buffer_async_read(struct buffer_head *bh);
static void ext2_page_write_checksum(struct page *page);
static void ext2_page_read_checksum(struct page *page);

//I did some nasty stuff here. I should probablly change linux/mpage.h
static struct bio *
mpage_alloc(struct block_device *bdev,
		sector_t first_sector, int nr_vecs,
		gfp_t gfp_flags)
{
	struct bio *bio;

	bio = bio_alloc(gfp_flags, nr_vecs);

	if(bio == NULL && (current->flags & PF_MEMALLOC)){
		while(!bio && (nr_vecs /= 2))
			bio = bio_alloc(gfp_flags, nr_vecs);
	}

	if(bio){
		bio->bi_bdev = bdev;
		bio->bi_sector = first_sector;
	}

	return bio;
}


static void map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block){
	struct inode *inode = page->mapping->host;
	struct buffer_head *page_bh, *head;
	int block = 0;

	if(!page_has_buffers(page)){
		if(inode->i_blkbits == PAGE_CACHE_SHIFT &&
				buffer_uptodate(bh)){
			SetPageUptodate(page);
			return;
		}
		create_empty_buffers(page,1 << inode->i_blkbits, 0);
	}
	head = page_buffers(page);
	page_bh = head;
	do{
		if(block == page_block){
			page_bh->b_state = bh->b_state;
			page_bh->b_bdev = bh->b_bdev;
			page_bh->b_blocknr = bh->b_blocknr;
			break;
		}
		page_bh = page_bh->b_this_page;
		block++;
	}while(page_bh != head);
}

/*
 * just a copy from buffer.c
 */
static void buffer_io_error(struct buffer_head *bh)
{
	char b[BDEVNAME_SIZE];

	printk(KERN_ERR "Buffer I/O error on device %s, logical block %Lu\n",
			bdevname(bh->b_bdev,b),
			(unsigned long long)bh->b_blocknr);
}



/*
 * Test whether an inode is a fast symlink.
 */
static inline int ext2_inode_is_fast_symlink(struct inode *inode)
{
	int ea_blocks = EXT2_I(inode)->i_file_acl ?
		(inode->i_sb->s_blocksize >> 9) : 0;

	return (S_ISLNK(inode->i_mode) &&
		inode->i_blocks - ea_blocks == 0);
}

/*
 * Called at the last iput() if i_nlink is zero.
 */
void ext2_delete_inode (struct inode * inode)
{
	truncate_inode_pages(&inode->i_data, 0);

	if (is_bad_inode(inode))
		goto no_delete;
	EXT2_I(inode)->i_dtime	= get_seconds();
	mark_inode_dirty(inode);
	ext2_write_inode(inode, inode_needs_sync(inode));

	inode->i_size = 0;
	if (inode->i_blocks)
		ext2_truncate (inode);
	ext2_free_inode (inode);

	return;
no_delete:
	clear_inode(inode);	/* We must guarantee clearing of inode... */
}

typedef struct {
	__le32	*p;
	__le32	key;
	struct buffer_head *bh;
} Indirect;

static inline void add_chain(Indirect *p, struct buffer_head *bh, __le32 *v)
{
	p->key = *(p->p = v);
	p->bh = bh;
}


/*
 * here *(from -> p) is basically the inode info of the logical block number
 * from -> key is the block number we got previously
 * if these two don't match
 * we can say the the file/inode has been changed
 * yangsuli
 */
static inline int verify_chain(Indirect *from, Indirect *to)
{
	while (from <= to && from->key == *from->p)
		from++;
	return (from > to);
}

/**
 *	ext2_block_to_path - parse the block number into array of offsets
 *	@inode: inode in question (we are only interested in its superblock)
 *	@i_block: block number to be parsed
 *	@offsets: array to store the offsets in
 *      @boundary: set this non-zero if the referred-to block is likely to be
 *             followed (on disk) by an indirect block.
 *	To store the locations of file's data ext2 uses a data structure common
 *	for UNIX filesystems - tree of pointers anchored in the inode, with
 *	data blocks at leaves and indirect blocks in intermediate nodes.
 *	This function translates the block number into path in that tree -
 *	return value is the path length and @offsets[n] is the offset of
 *	pointer to (n+1)th node in the nth one. If @block is out of range
 *	(negative or too large) warning is printed and zero returned.
 *
 *	Note: function doesn't find node addresses, so no IO is needed. All
 *	we need to know is the capacity of indirect blocks (taken from the
 *	inode->i_sb).
 */

/*
 * Portability note: the last comparison (check that we fit into triple
 * indirect block) is spelled differently, because otherwise on an
 * architecture with 32-bit longs and 8Kb pages we might get into trouble
 * if our filesystem had 8Kb blocks. We might use long long, but that would
 * kill us on x86. Oh, well, at least the sign propagation does not matter -
 * i_block would have to be negative in the very beginning, so we would not
 * get there at all.
 */

/* given a block, find the path
 * no actual I/0 performed
 * no need to change since EXT2_ADDR_PER_BLOCK_BITS is properly set
 * yangsuli
 */
static int ext2_block_to_path(struct inode *inode,
			long i_block, int offsets[4], int *boundary)
{
	int ptrs = EXT2_ADDR_PER_BLOCK(inode->i_sb);
	int ptrs_bits = EXT2_ADDR_PER_BLOCK_BITS(inode->i_sb);
	const long direct_blocks = EXT2_NDIR_BLOCKS,
		indirect_blocks = ptrs,
		double_blocks = (1 << (ptrs_bits * 2));
	int n = 0;
	int final = 0;

	if (i_block < 0) {
		ext2_msg(inode->i_sb, KERN_WARNING,
			"warning: %s: block < 0", __func__);
	} else if (i_block < direct_blocks) {
		offsets[n++] = i_block;
		final = direct_blocks;
	} else if ( (i_block -= direct_blocks) < indirect_blocks) {
		offsets[n++] = EXT2_IND_BLOCK;
		offsets[n++] = i_block;
		final = ptrs;
	} else if ((i_block -= indirect_blocks) < double_blocks) {
		offsets[n++] = EXT2_DIND_BLOCK;
		offsets[n++] = i_block >> ptrs_bits;
		offsets[n++] = i_block & (ptrs - 1);
		final = ptrs;
	} else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
		offsets[n++] = EXT2_TIND_BLOCK;
		offsets[n++] = i_block >> (ptrs_bits * 2);
		offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
		offsets[n++] = i_block & (ptrs - 1);
		final = ptrs;
	} else {
		ext2_msg(inode->i_sb, KERN_WARNING,
			"warning: %s: block is too big", __func__);
	}
	if (boundary)
		*boundary = final - 1 - (i_block & (ptrs - 1));

	return n;
}

/**
 *	ext2_get_branch - read the chain of indirect blocks leading to data
 *	@inode: inode in question
 *	@depth: depth of the chain (1 - direct pointer, etc.)
 *	@offsets: offsets of pointers in inode/indirect blocks
 *	@chain: place to store the result
 *	@err: here we store the error value
 *
 *	Function fills the array of triples <key, p, bh> and returns %NULL
 *	if everything went OK or the pointer to the last filled triple
 *	(incomplete one) otherwise. Upon the return chain[i].key contains
 *	the number of (i+1)-th block in the chain (as it is stored in memory,
 *	i.e. little-endian 32-bit), chain[i].p contains the address of that
 *	number (it points into struct inode for i==0 and into the bh->b_data
 *	for i>0) and chain[i].bh points to the buffer_head of i-th indirect
 *	block for i>0 and NULL for i==0. In other words, it holds the block
 *	numbers of the chain, addresses they were taken from (and where we can
 *	verify that chain did not change) and buffer_heads hosting these
 *	numbers.
 *
 *	Function stops when it stumbles upon zero pointer (absent block)
 *		(pointer to last triple returned, *@err == 0)
 *	or when it gets an IO error reading an indirect block
 *		(ditto, *@err == -EIO)
 *	or when it notices that chain had been changed while it was reading
 *		(ditto, *@err == -EAGAIN)
 *	or when it reads all @depth-1 indirect blocks successfully and finds
 *	the whole chain, all way to the data (returns %NULL, *err == 0).
 */


/**
  * This function fills chain[4] with actual data read from disk
  * offsets is the path to the block
  * note: if no block, return pointer to the  last filled triple
  * changed
  * yangsuli
  */
static Indirect *ext2_get_branch(struct inode *inode,
				 int depth,
				 int *offsets,
				 Indirect chain[4],
				 int *err)
{
	struct super_block *sb = inode->i_sb;
	Indirect *p = chain;
	struct buffer_head *bh;

	*err = 0;
	/* i_data is not going away, no lock needed */
	add_chain (chain, NULL, EXT2_I(inode)->i_data + (*offsets)*2);
	if (!p->key)
		goto no_block;
	while (--depth) {
		// read in the block data
		bh = sb_bread(sb, le32_to_cpu(p->key));
		if (!bh)
			goto failure;
		read_lock(&EXT2_I(inode)->i_meta_lock);
		if (!verify_chain(chain, p))
			goto changed;
		add_chain(++p, bh, (__le32*)bh->b_data + (*++offsets)*2);
		read_unlock(&EXT2_I(inode)->i_meta_lock);
		if (!p->key)
			goto no_block;
	}
	return NULL;

changed:
	read_unlock(&EXT2_I(inode)->i_meta_lock);
	brelse(bh);
	*err = -EAGAIN;
	goto no_block;
failure:
	*err = -EIO;
no_block:
	return p;
}

/**
 *	ext2_find_near - find a place for allocation with sufficient locality
 *	@inode: owner
 *	@ind: descriptor of indirect block.
 *
 *	This function returns the preferred place for block allocation.
 *	It is used when heuristic for sequential allocation fails.
 *	Rules are:
 *	  + if there is a block to the left of our position - allocate near it.
 *	  + if pointer will live in indirect block - allocate near that block.
 *	  + if pointer will live in inode - allocate in the same cylinder group.
 *
 * In the latter case we colour the starting block by the callers PID to
 * prevent it from clashing with concurrent allocations for a different inode
 * in the same block group.   The PID is used here so that functionally related
 * files will be close-by on-disk.
 *
 *	Caller must make sure that @ind is valid and will stay that way.
 */

/* I guess this function returns the block before the one one can allocate
 * not quite sure though...
 * TODO
 * yangsuli
 */

static ext2_fsblk_t ext2_find_near(struct inode *inode, Indirect *ind)
{
	struct ext2_inode_info *ei = EXT2_I(inode);
	__le32 *start = ind->bh ? (__le32 *) ind->bh->b_data : ei->i_data;
	__le32 *p;
	ext2_fsblk_t bg_start;
	ext2_fsblk_t colour;

	/* Try to find previous block */
	for(p = ind->p - 2; p >= start; p -= 2){
		if(*p)
			return le32_to_cpu(*p);
	}

	/* No such thing, so let's try location of indirect block */
	if (ind->bh)
		return ind->bh->b_blocknr;

	/*
	 * It is going to be refered from inode itself? OK, just put it into
	 * the same cylinder group then.
	 */
	bg_start = ext2_group_first_block_no(inode->i_sb, ei->i_block_group);
	colour = (current->pid % 16) *
			(EXT2_BLOCKS_PER_GROUP(inode->i_sb) / 16);
	return bg_start + colour;
}

/**
 *	ext2_find_goal - find a preferred place for allocation.
 *	@inode: owner
 *	@block:  block we want
 *	@partial: pointer to the last triple within a chain
 *
 *	Returns preferred place for a block (the goal).
 */

/* 
 * partically understood
 * yangsuli
 */
static inline ext2_fsblk_t ext2_find_goal(struct inode *inode, long block,
					  Indirect *partial)
{
	struct ext2_block_alloc_info *block_i;

	block_i = EXT2_I(inode)->i_block_alloc_info;

	/*
	 * try the heuristic for sequential allocation,
	 * failing that at least try to get decent locality.
	 */
	if (block_i && (block == block_i->last_alloc_logical_block + 1)
		&& (block_i->last_alloc_physical_block != 0)) {
		return block_i->last_alloc_physical_block + 1;
	}

	return ext2_find_near(inode, partial);
}

/**
 *	ext2_blks_to_allocate: Look up the block map and count the number
 *	of direct blocks need to be allocated for the given branch.
 *
 * 	@branch: chain of indirect blocks
 *	@k: number of blocks need for indirect blocks
 *	@blks: number of data blocks to be mapped.
 *	@blocks_to_boundary:  the offset in the indirect block
 *
 *	return the total number of blocks to be allocate, including the
 *	direct and indirect blocks.
 */

/*
 * need understood
 * yangsuli
 */
static int
ext2_blks_to_allocate(Indirect * branch, int k, unsigned long blks,
		int blocks_to_boundary)
{
	unsigned long count = 0;

	/*
	 * Simple case, [t,d]Indirect block(s) has not allocated yet
	 * then it's clear blocks on that path have not allocated
	 */
	if (k > 0) {
		/* right now don't hanel cross boundary allocation */
		if (blks < blocks_to_boundary + 1)
			count += blks;
		else
			count += blocks_to_boundary + 1;
		return count;
	}

	count++;

	/*
	 * note that when k = 0, i.e we have all the indrect blocks but not the data block
	 * branch[0] will be the indrect block which contains the pointer to the data block
	 * stop when 1. blks has been reached
	             2. reach the boundary
		     3. the file has a hole, we have now reached the boundary of the hole
         */
	while (count < blks && count <= blocks_to_boundary
		&& le32_to_cpu(*(branch[0].p + count * 2)) == 0) {
		count++;
	}
	return count;
}

/**
 *	ext2_alloc_blocks: multiple allocate blocks needed for a branch
 *	@indirect_blks: the number of blocks need to allocate for indirect
 *			blocks
 *
 *	@new_blocks: on return it will store the new block numbers for
 *	the indirect blocks(if needed) and the first direct block,
 *	@blks:	on return it will store the total number of allocated
 *		direct blocks
 */


/*
 * went through
 * yangsuli
 */
static int ext2_alloc_blocks(struct inode *inode,
			ext2_fsblk_t goal, int indirect_blks, int blks,
			ext2_fsblk_t new_blocks[4], int *err)
{
	int target, i;
	unsigned long count = 0;
	int index = 0;
	ext2_fsblk_t current_block = 0;
	int ret = 0;

	/*
	 * Here we try to allocate the requested multiple blocks at once,
	 * on a best-effort basis.
	 * To build a branch, we should allocate blocks for
	 * the indirect blocks(if not allocated yet), and at least
	 * the first direct block of this branch.  That's the
	 * minimum number of blocks need to allocate(required)
	 */
	target = blks + indirect_blks;

	while (1) {
		count = target;
		/* allocating blocks for indirect blocks and direct blocks */
		/* essentially set the bitmap
		 * so no need to change this ext2_new_blocks function
		 * yangsuli
		 */
		current_block = ext2_new_blocks(inode,goal,&count,err);
		if (*err)
			goto failed_out;

		target -= count;
		/* allocate blocks for indirect blocks */
		while (index < indirect_blks && count) {
			new_blocks[index++] = current_block++;
			count--;
		}

		if (count > 0)
			break;
	}

	/* save the new block number for the first direct block */
	new_blocks[index] = current_block;

	/* total number of blocks allocated for direct blocks */
	ret = count;
	*err = 0;
	return ret;
failed_out:
	for (i = 0; i <index; i++)
		ext2_free_blocks(inode, new_blocks[i], 1);
	return ret;
}

/**
 *	ext2_alloc_branch - allocate and set up a chain of blocks.
 *	@inode: owner
 *	@num: depth of the chain (number of blocks to allocate)
 *	@offsets: offsets (in the blocks) to store the pointers to next.
 *	@branch: place to store the chain in.
 *
 *	This function allocates @num blocks, zeroes out all but the last one,
 *	links them into chain and (if we are synchronous) writes them to disk.
 *	In other words, it prepares a branch that can be spliced onto the
 *	inode. It stores the information about that chain in the branch[], in
 *	the same format as ext2_get_branch() would do. We are calling it after
 *	we had read the existing part of chain and partial points to the last
 *	triple of that (one with zero ->key). Upon the exit we have the same
 *	picture as after the successful ext2_get_block(), excpet that in one
 *	place chain is disconnected - *branch->p is still zero (we did not
 *	set the last link), but branch->key contains the number that should
 *	be placed into *branch->p to fill that gap.
 *
 *	If allocation fails we free all blocks we've allocated (and forget
 *	their buffer_heads) and return the error value the from failed
 *	ext2_alloc_block() (normally -ENOSPC). Otherwise we set the chain
 *	as described above and return 0.
 */

/*
 * allocate the rest of a complete branch
 * changed to take into account checksum
 * yangsuli
 */
static int ext2_alloc_branch(struct inode *inode,
			int indirect_blks, int *blks, ext2_fsblk_t goal,
			int *offsets, Indirect *branch)
{
	int blocksize = inode->i_sb->s_blocksize;
	int i, n = 0;
	int err = 0;
	struct buffer_head *bh;
	int num;
	ext2_fsblk_t new_blocks[4];
	ext2_fsblk_t current_block;

	num = ext2_alloc_blocks(inode, goal, indirect_blks,
				*blks, new_blocks, &err);
	if (err)
		return err;

	branch[0].key = cpu_to_le32(new_blocks[0]);
	/*
	 * metadata blocks and data blocks are allocated.
	 */
	for (n = 1; n <= indirect_blks;  n++) {
		/*
		 * Get buffer_head for parent block, zero it out
		 * and set the pointer to new one, then send
		 * parent to disk.
		 */
		bh = sb_getblk(inode->i_sb, new_blocks[n-1]);
		branch[n].bh = bh;
		lock_buffer(bh);
		memset(bh->b_data, 0, blocksize);
		branch[n].p = (__le32 *) bh->b_data + offsets[n] * 2; //take into account the checksum yangsuli
		branch[n].key = cpu_to_le32(new_blocks[n]);
		*branch[n].p = branch[n].key;
		*(branch[n].p + 1) = cpu_to_le32(MAGIC_CHECKSUM);
		if ( n == indirect_blks) {
			current_block = new_blocks[n];
			/*
			 * End of chain, update the last new metablock of
			 * the chain to point to the new allocated
			 * data blocks numbers
			 */
                        /*
			for (i=1; i < num; i++)
				*(branch[n].p + i) = cpu_to_le32(++current_block);
			*/
			for (i=1; i < num; i++){
				*(branch[n].p + 2*i) = cpu_to_le32(++current_block);
				*(branch[n].p + 2*i + 1) = cpu_to_le32(MAGIC_CHECKSUM);
	                 	//here need to change checksum accordingly
			}
		}
		set_buffer_uptodate(bh);
		unlock_buffer(bh);
		mark_buffer_dirty_inode(bh, inode);
		/* We used to sync bh here if IS_SYNC(inode).
		 * But we now rely upon generic_write_sync()
		 * and b_inode_buffers.  But not for directories.
		 */
		if (S_ISDIR(inode->i_mode) && IS_DIRSYNC(inode))
			sync_dirty_buffer(bh);
	}
	*blks = num;
	return err;
}

/**
 * ext2_splice_branch - splice the allocated branch onto inode.
 * @inode: owner
 * @block: (logical) number of block we are adding
 * @where: location of missing link
 * @num:   number of indirect blocks we are adding
 * @blks:  number of direct blocks we are adding
 *
 * This function fills the missing link and does all housekeeping needed in
 * inode (->i_blocks, etc.). In case of success we end up with the full
 * chain to new block and return 0.
 */

/*
 * changed
 * need confirmation
 * yangsuli
 */
static void ext2_splice_branch(struct inode *inode,
			long block, Indirect *where, int num, int blks)
{
	int i;
	struct ext2_block_alloc_info *block_i;
	ext2_fsblk_t current_block;

	block_i = EXT2_I(inode)->i_block_alloc_info;

	/* XXX LOCKING probably should have i_meta_lock ?*/
	/* That's it */

	*where->p = where->key;

	/*
	 * Update the host buffer_head or inode to point to more just allocated
	 * direct blocks blocks
	 */
	if (num == 0 && blks > 1) {
		current_block = le32_to_cpu(where->key) + 1;
		for (i = 1; i < blks; i++){//checksum change yangsuli
			/*
			if(!where->bh){
				*(where->p + i ) = cpu_to_le32(current_block++);
			}else{
				*(where->p + 2*i) = cpu_to_le32(current_block++);
			}*/
			*(where->p + 2 * i) = cpu_to_le32(current_block++);
			*(where->p + 2 * i + 1) = cpu_to_le32(MAGIC_CHECKSUM); 
		}
	}

	/*
	 * update the most recently allocated logical & physical block
	 * in i_block_alloc_info, to assist find the proper goal block for next
	 * allocation
	 */
	if (block_i) {
		block_i->last_alloc_logical_block = block + blks - 1;
		block_i->last_alloc_physical_block =
				le32_to_cpu(where[num].key) + blks - 1;
	}

	/* We are done with atomic stuff, now do the rest of housekeeping */

	/* had we spliced it onto indirect block? */
	if (where->bh)
		mark_buffer_dirty_inode(where->bh, inode);

	inode->i_ctime = CURRENT_TIME_SEC;
	mark_inode_dirty(inode);
}

/*
 * Allocation strategy is simple: if we have to allocate something, we will
 * have to go the whole way to leaf. So let's do it before attaching anything
 * to tree, set linkage between the newborn blocks, write them if sync is
 * required, recheck the path, free and repeat if check fails, otherwise
 * set the last missing link (that will protect us from any truncate-generated
 * removals - all blocks on the path are immune now) and possibly force the
 * write on the parent block.
 * That has a nice additional property: no special recovery from the failed
 * allocations is needed - we simply release blocks and do not touch anything
 * reachable from inode.
 *
 * `handle' can be NULL if create == 0.
 *
 * return > 0, # of blocks mapped or allocated.
 * return = 0, if plain lookup failed.
 * return < 0, error case.
 */

 /*
  * changed
  * need confirmation
  * yangsuli
  */
static int ext2_get_blocks(struct inode *inode,
			   sector_t iblock, unsigned long maxblocks,
			   struct buffer_head *bh_result,
			   int create)
{
	int err = -EIO;
	int offsets[4];
	Indirect chain[4];
	Indirect *partial;
	ext2_fsblk_t goal;
	int indirect_blks;
	int blocks_to_boundary = 0;
	int depth;
	struct ext2_inode_info *ei = EXT2_I(inode);
	int count = 0;
	ext2_fsblk_t first_block = 0;

	depth = ext2_block_to_path(inode,iblock,offsets,&blocks_to_boundary);

	if (depth == 0)
		return (err);

	partial = ext2_get_branch(inode, depth, offsets, chain, &err);
	/* Simplest case - block found, no allocation needed */
	if (!partial) {
		first_block = le32_to_cpu(chain[depth - 1].key);
		clear_buffer_new(bh_result); /* What's this do? */
		count++;
		/*map more blocks*/
		while (count < maxblocks && count <= blocks_to_boundary) {
			ext2_fsblk_t blk;

			if (!verify_chain(chain, chain + depth - 1)) {
				/*
				 * Indirect block might be removed by
				 * truncate while we were reading it.
				 * Handling of that case: forget what we've
				 * got now, go to reread.
				 */
				err = -EAGAIN;
				count = 0;
				break;
			}/*
			if(!chain[depth-1].bh){//within inode
				blk = le32_to_cpu(*(chain[depth-1].p + count));
			}else{//in indirect block
				blk = le32_to_cpu(*(chain[depth-1].p + 2*count));
			}//checksum change  yangsuli
			*/
			blk = le32_to_cpu(*(chain[depth-1].p + 2 * count));
			if (blk == first_block + count)
				count++;
			else
				break;
		}
		if (err != -EAGAIN)
			goto got_it;
	}

	/* Next simple case - plain lookup or failed read of indirect block */
	if (!create || err == -EIO)
		goto cleanup;

	mutex_lock(&ei->truncate_mutex);
	/*
	 * If the indirect block is missing while we are reading
	 * the chain(ext3_get_branch() returns -EAGAIN err), or
	 * if the chain has been changed after we grab the semaphore,
	 * (either because another process truncated this branch, or
	 * another get_block allocated this branch) re-grab the chain to see if
	 * the request block has been allocated or not.
	 *
	 * Since we already block the truncate/other get_block
	 * at this point, we will have the current copy of the chain when we
	 * splice the branch into the tree.
	 */
	if (err == -EAGAIN || !verify_chain(chain, partial)) {
		while (partial > chain) {
			brelse(partial->bh);
			partial--;
		}
		partial = ext2_get_branch(inode, depth, offsets, chain, &err);
		if (!partial) {
			count++;
			mutex_unlock(&ei->truncate_mutex);
			if (err)
				goto cleanup;
			clear_buffer_new(bh_result);
			goto got_it;
		}
	}

	/*
	 * Okay, we need to do block allocation.  Lazily initialize the block
	 * allocation info here if necessary
	*/
	if (S_ISREG(inode->i_mode) && (!ei->i_block_alloc_info))
		ext2_init_block_alloc_info(inode);

	goal = ext2_find_goal(inode, iblock, partial);

	/* the number of blocks need to allocate for [d,t]indirect blocks */
	indirect_blks = (chain + depth) - partial - 1;
	/*
	 * Next look up the indirect map to count the totoal number of
	 * direct blocks to allocate for this branch.
	 */
	count = ext2_blks_to_allocate(partial, indirect_blks,
					maxblocks, blocks_to_boundary);
	/*
	 * XXX ???? Block out ext2_truncate while we alter the tree
	 */
	err = ext2_alloc_branch(inode, indirect_blks, &count, goal,
				offsets + (partial - chain), partial);

	if (err) {
		mutex_unlock(&ei->truncate_mutex);
		goto cleanup;
	}

	if (ext2_use_xip(inode->i_sb)) {
		/*
		 * we need to clear the block
		 */
		err = ext2_clear_xip_target (inode,
			le32_to_cpu(chain[depth-1].key));
		if (err) {
			mutex_unlock(&ei->truncate_mutex);
			goto cleanup;
		}
	}

	ext2_splice_branch(inode, iblock, partial, indirect_blks, count);
	mutex_unlock(&ei->truncate_mutex);
	set_buffer_new(bh_result);
got_it:
	map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key));
	if (count > blocks_to_boundary)
		set_buffer_boundary(bh_result);
	err = count;
	/* Clean up and exit */
	partial = chain + depth - 1;	/* the whole chain */
cleanup:
	while (partial > chain) {
		brelse(partial->bh);
		partial--;
	}
	return err;
}

/*
 * locate a block holding data for an ext2 regular file
 * if the block does not exist, the fnction automatically allocates the block to the file
 * I haven't read the function yet, the above is from ULK
 * yangsuli
 */
int ext2_get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh_result, int create)
{
	unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
	int ret = ext2_get_blocks(inode, iblock, max_blocks,
			      bh_result, create);
	if (ret > 0) {
		bh_result->b_size = (ret << inode->i_blkbits);
		ret = 0;
	}
	return ret;

}

int ext2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
		u64 start, u64 len)
{
	return generic_block_fiemap(inode, fieinfo, start, len,
				    ext2_get_block);
}

static int ext2_writepage(struct page *page, struct writeback_control *wbc)
{
	return ext2_block_write_full_page(page, ext2_get_block, wbc);
}

int ext2_block_write_full_page(struct page *page, get_block_t *get_block,
		struct writeback_control *wbc)
{
	return block_write_full_page_endio(page,get_block,wbc,
			ext2_end_buffer_async_write);
}

static void ext2_page_write_checksum(struct page *page){
	struct inode *inode = page->mapping->host;
	const unsigned blkbits = inode->i_blkbits;
	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
	const unsigned blocksize = 1 << blkbits;
	sector_t block_in_file;
	sector_t last_block;
	sector_t last_block_in_file;
	sector_t curr_block;
	int checksum;

	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
	last_block = block_in_file + blocks_per_page;
	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;

	if(last_block > last_block_in_file)
		last_block = last_block_in_file;

	kaddr = kmap_atomic(page, KM_USER0);
	for(curr_block = block_in_file; curr_block <= last_block; curr_block++,kaddr += blocksize){
		checksum = ext2_compute_checksum(kaddr,blocksize);
		ext2_write_checksum(inode, curr_block, checksum);
	}

	kunmap_atomic(kaddr,KM_USER0);
}

void ext2_write_checksum(struct inode *inode, sector_t iblock, int checksum)
{
	struct ext2_inode_info *ei = EXT2_I(inode);
	int offsets[4];
	Indirect chain[4];
	Indirect *partial;
	int depth;
	ext2_fsblk_t dest_block;
	struct buffer_head *bh;

	depth = ext2_block_to_path(inode,iblock,offsets,NULL);

	if(depth == 0)
		return -EIO;

	if( (--depth) == 0){
		//inside inode
		ei->i_data[iblock * 2 + 1] = cpu_to_le32(checksum);
		mark_inode_dirty(inode);
		return;
	}

	partial = ext2_get_branch(inode,depth,offsets,chain,&err);

	//if partial != NULL, possiblly a hole in file
	if(partial){
		//do nothing
		return;
	}

	//chain has been changed, possiblly a truncating going on
	//do nothing 
	if(! verify_chain(chain, chain + depth - 1)){
		return;
	}

	dest_block = le32_to_cpu(chain[depth - 1].key);
	bh = sb_bread(inode->i_sb, dest_block);
	lock_buffer(bh);
	*(bh->b_data + offsets[depth] * 2 + 1) = cpu_to_le32(checksum);
	set_buffer_uptodate(bh); //shoud we do that here??
	unlock_buffer(bh);
	mark_buffer_dirty_inode(bh,inode);

	return;
}

void ext2_end_buffer_async_write(struct buffer_head *bh, int uptodate)
{
	char b[BDEVNAME_SIZE];
	unsigned long flags;
	struct buffer_head *first;
	struct buffer_head *tmp;
	struct page *page;

	BUG_ON(!buffer_async_write(bh));

	page = bh->b_page;
	if(uptodate){
		set_buffer_uptodate(bh);
	}else{
		if(printk_ratelimit()){
			buffer_io_error(bh);
			printk(KERN_WARNING "lost page write due to I/O error on %s\n",
					bdevname(bh->b_bdev,b));
		}
		set_bit(AS_EIO, &page->mapping->flags);
		set_buffer_write_io_error(bh);
		clear_buffer_uptodate(bh);
		SetPageError(page);
	}

	first = page_buffers(page);
	local_irq_save(flags);
	bit_spin_lock(BH_Uptodate_Lock, &first->b_state);

	clear_buffer_async_write(bh);
	unlock_buffer(bh);
	tmp = bh->b_this_page;
	while(tmp != bh) {
		if(buffer_async_write(tmp)){
			BUG_ON(!buffer_locked(tmp));
			goto still_busy;
		}
		tmp = tmp->b_this_page;
	}
	bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
	local_irq_restore(flags);

	ext2_page_write_checksum(page);
	end_page_writeback(page);
	return;

still_busy:
	bit_spin_unlock(BH_Uptodate_Lock,&first->b_state);
	local_irq_restore(flags);
	return;
}

/*
 * The generic -> writepage function for buffer-backed address spaces
 * this form passes in the end_io handler used to finish the IO
 */
// int ext2_block_write_full_page_endio(struct page *page, get_block_t *get_block,
		// struct writeback_control *wbc, bh_end_io_t *handler)
// {
	// struct inode *const inode = page->mapping->host;
	// loff_t i_size = i_size_read(inode);
	// const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
// 
	// /* Is the page fully inside i_size? */
	// if(page->index < end_index)
		// //MYNOTE: TODO ext2 specific verison here????
		// return __block_write_full_page(inode, page, get_block,wbc,
				// handler);
// 
	// /* Is this page fully outside i_size? (truncate in progress) */
	// offset = i_size & (PAGE_CACHE_SHIFT -1);
	// if(page->index >= end_index+1 || !offset){
		// /*
		 // * The page may have dirty, unmapped buffers. For example,
		 // * They may have beed added in ext3_writepages(). Make them 
		 // * freeable here, so the page does not leak.
		 // */
		// do_invalidatepage(page,0);
		// unlock_page(page);
		// return 0; /* don't care*/
	// }
// 
	// /* The page straddles i_size. It must be zeroed out on each and every
	 // * writepage invokation because it may be mmapped. "A file is mapped
	 // * in multiples of the page size. For a file that is not a multiple of
	 // * the page size, the remaining memory is zeroed when mapped, and 
	 // * writes to that region are not written out to the file."
	 // */
	// zero_user_segment(page,offset, PAGE_CACHE_SIZE);
	// return __block_write_full_page(inode,page,get_block,wbc,handler);
// }

static int ext2_readpage(struct file *file, struct page *page)
{
	return ext2_mpage_readpage(page, ext2_get_block);

}

static int ext2_mpage_readpage(struct page *page, get_block_t get_block)
{
	struct bio *bio = NULL;
	sector_t last_block_in_bio = 0;
	struct buffer_head map_bh;
	unsigned long first_logical_block = 0;

	map_bh.b_state = 0;
	map_bh.b_size = 0;
	bio = ext2_do_mpage_readpage(bio, page, 1, &last_block_in_bio,
			&map_bh,&first_logical_block,get_block);
	if(bio)
		ext2_mpage_bio_submit(READ,bio);
	return 0;
}


/*
 * originial comments:
 * This is the worker routine which does all the work of mapping the disk
 * blocks and constructs the largest possible bios, submits them for IO if
 * the blocks are not contiguous on the disk
 *
 * We pass a buffer_head back and forth and use its buffer_mapped() flage to
 * represent the validity of its disk mapping and to decide when to do the 
 * next get_block() call.
 */
static struct bio *
ext2_do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
		sector_t *last_block_in_bio, struct buffer_head* map_bh,
		unsigned long *first_logical_block, get_block_t get_block)
{
	struct inode *inode = page->mapping->host;
	const unsigned blkbits = inode->i_blkbits;
	const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
	const unsigned blocksize = 1 << blkbits;
	sector_t block_in_file;
	sector_t last_block;
	sector_t last_block_in_file;
	sector_t blocks[MAX_BUF_PER_PAGE];
	unsigned page_block;
	unsigned first_hole = blocks_per_page;
	struct block_device *bdev = NULL;
	int length;
	int fully_mapped = 1;
	unsigned nblocks;
	unsigned relative_block;

	if(page_has_buffers(page))
		goto confused;

	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT -blkbits);
	last_block = block_in_file + nr_pages * blocks_per_page;
	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
	if(last_block > last_block_in_file)
		last_block = last_block_in_file;
	page_block = 0;

	/*
	 * Map blocks using the result of the previous get_blocks call first
	 */
	nblocks = map_bh->b_size >> blkbits;
	if(buffer_mapped(map_bh) && block_in_file > *first_logical_block && block_in_file < (*first_logical_block + nblocks)){
		unsigned map_offset = block_in_file - *first_logical_block;
		unsigned last = nblocks - map_offset;

		for(relative_block = 0; ; relative_block++){
			if(relative_block == last){
				clear_buffer_mapped(map_bh);
				break;
			}
			if(page_block == blocks_per_page)
				break;
			break;
			blocks[page_block] = map_bh->b_blocknr + map_offset +
				relative_block;
			page_block++;
			block_in_file++;
		}
		bdev = map_bh->b_bdev;
	}

	/*
	 * Then do more get_blocks calls until we are done with this page
	 */
	map_bh->b_page = page;
	while(page_block < blocks_per_page){
		map_bh->b_state = 0;
		map_bh->b_size = 0;

		if(block_in_file < last_block){
			map_bh->b_size = (last_block - block_in_file) << blkbits;
			if(get_block(inode, block_in_file, map_bh, 0))
				goto confused;
			*first_logical_block = block_in_file;
		}
		if(!buffer_mapped(map_bh)){
			fully_mapped = 0;
			if(first_hole == blocks_per_page)
				first_hole = page_block;
			page_block++;
			block_in_file++;
			continue;
		}

		/* some filesystems will copy data into the page during
		 * the get_block call, in which case we don't want to
		 * read it again. map_buffer_to_page copies the data
		 * we just collected from get_block into the page's
		 * buffers so readpage doesn't have to repeat the 
		 * get_block call
		 */
		if(buffer_uptodate(map_bh)){
			map_buffer_to_page(page,map_bh, page_block);
			goto confused;
		}

		if(first_hole != blocks_per_page)
			goto confused;    /*holes -> non-hole */

		/* contiguous blocks? */
		if(page_block && blocks[page_block -1] != map_bh->b_blocknr - 1)
			goto confused;
		nblocks = map_bh->b_size >> blkbits;
		for(relative_block = 0; ; relative_block++){
			if(relative_block == nblocks){
				clear_buffer_mapped(map_bh);
				break;
			}else if(page_block == blocks_per_page)
				break;
			blocks[page_block] = map_bh->b_blocknr + relative_block;
			page_block++;
			block_in_file++;
		}
		bdev = map_bh->b_bdev;
	}


	if(first_hole != blocks_per_page){
		zero_user_segment(page, first_hole << blkbits, PAGE_CACHE_SIZE);
		if(first_hole == 0){
			SetPageUptodate(page);
			unlock_page(page);
			goto out;
		}
	}else if(fully_mapped) {
		SetPageMappedToDisk(page);
	}

	/*
	 * This page will go to BIO. Do we need to send this BIO off first?
	 */
	if(bio && (*last_block_in_bio != blocks[0] - 1))
		bio = ext2_mpage_bio_submit(READ,bio);

alloc_new:
	if(bio == NULL){
		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
				min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
				GFP_KERNEL);
		if(bio == NULL)
			goto confused;
	}

	length = first_hole << blkbits;
	if(bio_add_page(bio,page,length,0) < length) {
		bio = ext2_mpage_bio_submit(READ,bio);
		goto alloc_new;
	}

	relative_block = block_in_file - *first_logical_block;
	nblocks = map_bh->b_size >> blkbits;
	if((buffer_boundary(map_bh) && relative_block == nblocks) || 
			(first_hole != blocks_per_page)){
		bio = ext2_mpage_bio_submit(READ, bio);
	}
	else
		*last_block_in_bio = blocks[blocks_per_page - 1];
out:
	return bio;
confused:
	if(bio)
		bio = ext2_mpage_bio_submit(READ,bio);
	if(!PageUptodate(page))
		ext2_block_read_full_page(page,get_block);
	else
		unlock_page(page);
	goto out;
}

/*
 * Generic "read page" function for block devices that have the normal
 * get_block functionality. This is most of the block device filesystem.
 * Reads the page asynchronously -- the unlock_buffer() and set/
 * clear_buffer_uptodate() functions propagate buffer state into the
 * page struct once IO has completed.
 */

int ext2_block_read_full_page(struct page *page, get_block_t *get_block)
{
	struct inode *inode = page->mapping->host;
	sector_t iblock, lblock;
	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
	unsigned int blocksize;
	int nr, i;
	int fully_mapped = 1;

	BUG_ON(!PageLocked(page));
	blocksize = 1 << inode->i_blkbits;
	if(!page_has_buffers(page))
		create_empty_buffers(page,blocksize,0);
	head = page_buffers(page);

	iblock = (sector_t)page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits);
	lblock = (i_size_read(inode)+blocksize-1) >> inode->i_blkbits;
	bh = head;
	nr = 0;
	i = 0;

	do{
		if(buffer_uptodate(bh))
			continue;

		if(!buffer_mapped(bh)){
			int err = 0;

			fully_mapped = 0;
			if(iblock < lblock){
				WARN_ON(bh->b_size != blocksize);
				err = get_block(inode, iblock, bh, 0);
				if(err)
					SetPageError(page);
			}
			if(!buffer_mapped(bh)){
				zero_user(page,i*blocksize,blocksize);
				if(!err){
					set_buffer_uptodate(bh);
				}
				continue;
			}

			if(buffer_uptodate(bh))
				continue;
		}
		arr[nr++] = bh;
	} while(i++, iblock++, (bh = bh->b_this_page));

	if(fully_mapped)
		SetPageMappedToDisk(page);

	if(!nr){
		/*
		 * All buffers are uptodate - we can set the page uptodate
		 * as well. But not if get_block() returned an error.
		 */
		if(!PageError(page))
			SetPageUptodate(page);
		unlock_page(page);
		return 0;
	}

	/*Stage two: lock the buffers */
	for(i = 0; i < nr; i++){
		bh = arr[i];
		lock_buffer(bh);
		//MYNOTE: to implement
		ext2_mark_buffer_async_read(bh);
	}

	/*
	 * Stage 3: start the IO. Check for uptodateness
	 * inside the buffer lock in case another process
	 * reading the underlying blockdev brought it uptodate
	 * (the sct fix).
	 */

	for(i = 0; i < nr; i++){
		bh = arr[i];
		if(buffer_uptodate(bh))
			ext2_end_buffer_async_read(bh,1);
		else
			//here submit_bh will call the bh->end_io completion method
			submit_bh(READ,bh);
	}
	return 0;
}

static void ext2_mark_buffer_async_read(struct buffer_head *bh)
{
	bh->b_end_io = ext2_end_buffer_async_read;
	set_buffer_async_read(bh);
}

static void ext2_end_buffer_async_read(struct buffer_head *bh, int uptodate)
{
	unsigned long flags;
	struct buffer_head *first;
	struct buffer_head *tmp;
	struct page *page;
	int page_uptodate = 1;

	BUG_ON(!buffer_async_read(bh));

	page = bh->b_page;
	if(uptodate){
		set_buffer_uptodate(bh);
	}else{
		clear_buffer_uptodate(bh);
		/*if(!quiet_error(bh))*/
		if(printk_ratelimit())
			buffer_io_error(bh);
		SetPageError(page);
	}

	/*
	 * be very careful from here on. Bad things can happen if
	 * two buffer heads end IO at almost the same time and both
	 * decide that the page is now completely done.
	 */
	first = page_buffers(page);
	local_irq_save(flags);
	bit_spin_lock(BH_Uptodate_Lock,&first->b_state);
	clear_buffer_async_read(bh);
	unlock_buffer(bh);
	tmp = bh;
	do{
		if(!buffer_uptodate(tmp))
			page_uptodate = 0;
		if(buffer_async_read(tmp)){
			BUG_ON(!buffer_locked(tmp));
			goto still_busy;
		}
		tmp = tmp->b_this_page;
	}while(tmp != bh);

	bit_spin_unlock(BH_Uptodate_Lock,&first->b_state);
	local_irq_restore(flags);

	/*
	 * if none of the buffers had errors and they are all
	 * uptodate then we can set the page uptodate.
	 */
	if(page_uptodate && !PageError(page)){
		ext2_page_read_checksum(page);
		SetPageUptodate(page);
	}
	unlock_page(page);
	return;

still_busy:
	bit_spin_unlock(BH_Uptodate_Lock,&first->b_state);
	local_irq_restore(flags);
	return;
}

static struct bio* ext2_mpage_bio_submit(int rw, struct bio *bio)
{
	bio->bi_end_io = ext2_mpage_end_io_read;
	if(rw == WRITE)
		bio->bi_end_io = ext2_mpage_end_io_write;
	submit_bio(rw,bio);
	return NULL;
}


static void ext2_mpage_end_io_write(struct bio *bio, int err){
	//MYNOTE: TODO
	//mpage_end_io_write(bio,err);
	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;

	do{
		struct page *page = bvec->bv_page;

		if(--bvec >= bio->bi_io_vec)
			prefetchw(&bvec->bv_page->flags);

		if(!uptodate){
			SetPageError(page);
			if(page->mapping)
				set_bit(AS_EIO, &page->mapping->flags);
		}
		ext2_page_write_checksum(page);
		end_page_writeback(page);
	}while(bvec >= bio->bi_io_vec);
	bio_put(bio);
}

static void ext2_page_read_checksum(struct page *page){

		struct inode *inode = page->mapping->host;
		const unsigned blkbits = inode->i_blkbits;
		const unsigned blocks_per_page = PAGE_CACHE_SIZE >> blkbits;
		const unsigned blocksize = 1 << blkbits;
		sector_t block_in_file;
		sector_t last_block;
		sector_t last_block_in_file;
		sector_t curr_block;
		int checksum, stored_checksum;
		char *kaddr;

		block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
		last_block = block_in_file + blocks_per_page;
		last_block_in_file = (i_size_read(inode) + blocksize -1) >>blkbits;
		if(last_block > last_block_in_file)
			last_block = last_block_in_file;

		kaddr = kmap_atomic(page, KM_USER0);
		for(curr_block = block_in_file; curr_block <= last_block; curr_block++, kaddr += blocksize){
			checksum = ext2_compute_checksum(kaddr, blocksize);
			stored_checksum = ext2_read_checksum(inode,curr_block);
			if(checksum != stored_checksum){
				ext2_msg(inode->i_sb, KERN_WARNING,
						"warning: %s: checksum doesn't match when reading", __func__);
			}
		}

		kunmap_atomic(kaddr, KM_USER0);

}

static void ext2_mpage_end_io_read(struct bio *bio, int err)
{
	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;

	do{
		struct page* page = bvec->bv_page;

		ext2_page_read_checksum(page);

		if(--bvec >= bio->bi_io_vec)
			prefetchw(&bvec->bv_page->flags);
		if(uptodate){
			SetPageUptodate(page);
			SetPageError(page);
		}
		unlock_page(page);
	}while(bvec >= bio->bi_io_vec);
	bio_put(bio);
/*
	ext2_msg(inode->i_sb, KERN_WARNING,
			"note: ext2_mpage_end_io_read called");
			*/
}


int ext2_compute_checksum(char *star, int size){
	return MAGIC_CHECKSUM;
}


//MYNOTE: possible we need another way to indicate error
//so that our checksum could be negative valued.
int ext2_read_checksum(struct inode *inode, sector_t iblock)
{
	struct ext2_inode_info *ei = EXT2_I(inode);
	int offsets[4];
	Indirect chain[4];
	Indirect *partial;
	int depth;
	ext2_fsblk_t dest_block;
	struct buffer_head *bh;
	int checksum;
	int err;

	//MYNOTE: here we can't supply NULL as the buffer_head
	//here we garatee that the block exists
	//if not, we allocate one
	/*
	err = ext2_get_block(inode, iblock, NULL, 1);

	if(err <= 0){
		return err;
	}
	*/

	//we supply NULL here bcz we don't need to know the boundary
	depth = ext2_block_to_path(inode,iblock, offsets,NULL);

	if(depth == 0)
		return -EIO;

	if((depth -= 1) == 0){
		//inside inode
		checksum = le32_to_cpu(ei->i_data[iblock * 2 + 1]);
	}

	partial = ext2_get_branch(inode,depth,offsets,chain,&err);
	
	// if partial == NULL, then it might be hole
	// unlikely though since it's in a bio
	// anyway, we don't need to read the checksum
	// in case it's a hole, we return the checksumm
	// for all-zero blocks;

	if(partial){
		//MYNOTE: should be ALL_0_CHECKSUM
		return MAGIC_CHECKSUM;
	}

	if(!verify_chain(chain,chain+depth-1)){
		//error
		return -EIO;
	}

	dest_block = le32_to_cpu(chain[depth - 1].key);
	//MYNOTE: here we should use bread instead of getblk
	//see ULK p615
	//bh = sb_getblk(inode->i_sb, dest_block);
	bh = sb_bread(inode->i_sb,dest_block);
	if(!bh){
		//deal with error here
		return -EIO;
	}
	checksum = le32_to_cpu(*(bh->b_data + offsets[depth] * 2 + 1));

	return checksum;
}


		





static int
ext2_readpages(struct file *file, struct address_space *mapping,
		struct list_head *pages, unsigned nr_pages)
{
	return ext2_mpage_readpages(mapping, pages, nr_pages, ext2_get_block);
}

int 
ext2_mpage_readpages(struct address_space *mapping, struct list_head *pages,
		unsigned nr_pages, get_block_t get_block)
{
	struct bio *bio = NULL;
	unsigned page_idx;
	sector_t last_block_in_bio = 0;
	struct buffer_head map_bh;
	unsigned long first_logical_block = 0;

	map_bh.b_state = 0;
	map_bh.b_size = 0;
	for(page_idx = 0; page_idx < nr_pages; page_idx++){
		struct page *page = list_entry(pages->prev, struct page,lru);

		prefetchw(&page->flags);
		list_del(&page->lru);
		if(!add_to_page_cache_lru(page,mapping,
					page->index, GFP_KERNEL)){
			bio = ext2_do_mpage_readpage(bio,page,
					nr_pages - page_idx,
					&last_block_in_bio, &map_bh,
					&first_logical_block,
					get_block);
		}
		page_cache_release(page);
	}
	BUG_ON(!list_empty(pages));
	if(bio)
		ext2_mpage_bio_submit(READ,bio);
	return 0;
}

int __ext2_write_begin(struct file *file, struct address_space *mapping,
		loff_t pos, unsigned len, unsigned flags,
		struct page **pagep, void **fsdata)
{
	return block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
							ext2_get_block);
}

static int
ext2_write_begin(struct file *file, struct address_space *mapping,
		loff_t pos, unsigned len, unsigned flags,
		struct page **pagep, void **fsdata)
{
	*pagep = NULL;
	return __ext2_write_begin(file, mapping, pos, len, flags, pagep,fsdata);
}

static int
ext2_nobh_write_begin(struct file *file, struct address_space *mapping,
		loff_t pos, unsigned len, unsigned flags,
		struct page **pagep, void **fsdata)
{
	/*
	 * Dir-in-pagecache still uses ext2_write_begin. Would have to rework
	 * directory handling code to pass around offsets rather than struct
	 * pages in order to make this work easily.
	 */
	return nobh_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
							ext2_get_block);
}

static int ext2_nobh_writepage(struct page *page,
			struct writeback_control *wbc)
{
	return ext2_nobh_writepage(page, ext2_get_block, wbc);
}

int ext2_nobh_writepage(struct page *page, get_block_t *get_block,
		struct writeback_control *wbc)
{
	struct inode *const inode = page->mapping->host;
	loff_t i_size = i_size_read(inode);
	const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
	unsigned offset;
	int ret;

	/* Is this page fully inside i_size? */
	if (page->index < end_index)
		goto out;

	/* Is the page fully outside i_size? (truncate in progress)*/
	offset = i_size & (PAGE_CACHE_SIZE-1);
	if(page->index >= end_index+1 || !offset){
#if 0
		if(page->mapping->a_ops->invalidatepage)
			page->mapping->a_ops->invalidatepage(page,offset);
#endif
		unlock_page(page);
		return 0; /*don't care*/
	}
	zero_user_segment(page,offset,PAGE_CACHE_SIZE);
out:
	ret = ext2_mpage_writepages(page,get_block,wbc);
	if(ret == -EAGAIN)
		ret = __block_write_full_page(inode,page,get_block,wbc,
				ext2_end_buffer_async_write);
	return ret;
}

static sector_t ext2_bmap(struct address_space *mapping, sector_t block)
{
	return generic_block_bmap(mapping,block,ext2_get_block);
}

static ssize_t
ext2_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
			loff_t offset, unsigned long nr_segs)
{
	struct file *file = iocb->ki_filp;
	struct inode *inode = file->f_mapping->host;

	return blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
				offset, nr_segs, ext2_get_block, NULL);
}

static int
ext2_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
	return ext2_mpage_writepages(mapping, wbc, ext2_get_block);
}

struct mpage_data {
	struct bio *bio;
	sector_t last_block_in_bio;
	get_block_t *get_block;
	unsigned use_writepage;
};

int
ext2_mpage_writepages(struct address_space *mapping,
		struct writeback_control *wbc, get_block_t get_block)
{
	int ret;

	//this never happens
	if(!get_block)
		ret = generic_writepages(mapping,wbc);
	else{
		struct mpage_data mpad = {
			.bio = NULL,
			.last_block_in_bio = 0,
			.get_block = get_block,
			.use_writepage = 1,
		};

		ret = write_cache_pages(mapping,wbc, __ext2_mpage_writepage, &mpd);

		if(mpd.bio){
			ext2_mpage_bio_submit(WRITE,mpd.bio);
		}
	}

	return ret;
}


static int __ext2_mpage_writepage(struct page *page, struct writeback_control *wbc, void *data)
{
	struct mpage_data *mpd = data;
	struct bio *bio = mpd->bio;
	struct address_space *mapping = page->mapping;
	struct inode *inode = page->mapping->host;
	const unsigned blkbits = inode->i_blkbits;
	unsigned long end_index;
	const unsigned blocks_per_page  = PAGE_CACHE_SIZE >> blkbits;
	sector_t last_block;
	sector_t block_in_file;
	sector_t blocks[MAX_BUF_PER_PAGE];
	unsigned page_block;
	unsigned first_unmapped = blocks_per_page;
	struct block_device *bdev = NULL;
	int boundary = 0;
	sector_t boundary_block = 0;
	struct block_device *boundary_bdev = NULL;
	int length;
	struct buffer_head map_bh;
	loff_t i_size = i_size_read(inode);
	int ret = 0;

	if(page_has_buffers(page)){
		struct buffer_head *head = page_buffers(page);
		struct buffer_head *bh = head;

		/*If they're all mapped and dirty, do it*/
		page_block = 0;
		do{
			BUG_ON(buffer_locked(bh));
			if(!buffer_mapped(bh)){
				/*
				 * unmapped dirty buffers are created by
				 * __set_page_dirty_buffers->mmapped data
				 */
				if(buffer_dirty(bh))
					goto confused;
				if(first_unmapped == blocks_per_page)
					first_unmapped = page_block;
				continue;
			}

			if(first_unmapped != blocks_per_page)
				goto confused; /*hole -> non-hole*/

			if(!buffer_dirty(bh) || !buffer_uptodate(bh))
				goto confused;
			if(page_block){
				if(bh->b_blocknr != blocks[page_block-1]+1)
					goto confused;
			}
			blocks[page_block++] = bh->b_blocknr;
			boundary = buffer_boundary(bh);
			if(boundary){
				boundary_block = bh->b_blocknr;
				boundary_bdev = bh->b_bdev;
			}
			bdev = bh->b_bdev;
		}while((bh =  bh->b_this_page) != head);

		if(first_unmapped)
			goto page_is_mapped;

		/*
		 * Page has buffers, but they are all unmapped. Tha page was
		 * created by pagein or read over a hole which was handled by 
		 *block_read_full_page(). If this address_space is also 
		 *using mpage_readpages then this can rarely happen.
		 */
		goto confused;
	}

	/*
	 *This page has no buffers: map it to disk
	 */
	BUG_ON(!PageUptodate(page));
	block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
	last_block = (i_size - 1) >> blkbits;
	map_bh.b_page = page;
	for(page_block = 0; page_block < blocks_per_page; ){
		map_bh.b_state = 0;
		map_bh.b_size = 1 << blkbits;
		if(mpd->get_block(inode,block_in_file,&map_bh,1))
			goto confused;
		if(buffer_new(&map_bh))
			unmap_underlying_metadata(map_bh,b_bdev,
					map_bh.b_blocknr);
		if(buffer_boundary(&map_bh)){
			boundary_block = map_bh.b_blocknr;
			boundary_bdev = map_bh.b_bdev;
		}
		if(page_block){
			if(map_bh.b_blocknr != blocks[page_block-1] + 1)
				goto confused;
		}
		blocks[page_block++] = map_bh.b_blocknr;
		boundary = buffer_boundary(&map_bh);
		bdev = map_bh.b_bdev;
		if(block_in_file == last_block)
			break;
		block_in_file++;
	}
	BUG_ON(page_block == 0);

	first_unmapped = page_block;

page_is_mapped:
	end_index = i_size >> PAGE_CACHE_SHIFT;
	if(page->index >= end_index){
		unsigned offset = i_size & (PAGE_CACHE_SIZE - 1);

		if(page->index > end_index || !offset)
			goto confused;
		zero_user_segment(page,offset,PAGE_CACHE_SIZE);
	}

	/*
	 * This page will go to BIO. Do we need to send this BIO off first?
	 */
	/*
	 * MYNOTE: when we are sending the previous BIO, should it be ext2 specific???
	 */
	if(bio && mpd->last_block_in_bio != blocks[0] - 1)
		bio = ext2_mpage_bio_submit(WRITE,bio);

alloc_new:
	if(bio == NULL){
		bio = mpage_alloc(bdev,blocks[0] << (blkbits - 9),
				bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
		if(bio == NULL)
			goto confused;
	}

	length = first_unmapped << blkbits;
	if(bio_add_page(bio,page,length,0) < length){
		bio = ext2_mpage_bio_submit(WRITE,bio);
		goto alloc_new;
	}

	if(page_has_buffers(page)){
		struct buffer_head *head = page_buffers(page);
		struct buffer_head *bh = head;
		unsigned buffer_counter = 0;

		do{
			if(buffer_counter++ == first_unmapped)
				break;
			clear_buffer_dirty(bh);
			bh = bh->b_this_page;
		}while(bh != head);

		/*
		 * we cannot drop the bh if the page is not uptodate
		 * or a concurrent readpage would fail to serialize with the bh
		 * and it would read from disk befor we reach the platter.
		 */
		if(buffer_heads_over_limit && PageUptodate(page))
			try_to_free_buffers(page);
	}

	BUG_ON(PageWriteback(page));
	set_page_writeback(page);
	unlock_page(page);
	if(boundary || (first_unmapped != blocks_per_page)){
		bio = ext2_mpage_bio_submit(WRITE,bio);
		if(boundary_block){
			//MYNOTE: TODO
			//we may need an ext2 sepcific verison of write_boundary_block()
			write_boundary_block(boundary_bdev,
					boundary_block, 1 << blkbits);
		}
	}else{
		mpd->last_block_in_bio = blocks[blocks_per_page - 1];
	}
	goto out;

confused:
	if(bio)
		bio = ext2_mpage_bio_submit(WRITE,bio);

	if(mpd->use_writepage){
		ret = mapping->a_ops->writepage(page,wbc);
	}else{
		ret = -EAGAIN;
		goto *out;
	}

	mapping_set_error(mapping,ret);
out:
	mpd->bio = bio;
	return ret;
}


/*
int ext2_write_cache_pages(struct address_space *mapping,
		struct writeback_control *wbc, writepage_t writepage,
		void *data)
{
	int ret = 0;
	int done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t uninitialized_var(writeback_index);
	pgoff_t index;
	pgoff_t end; 
	pgoff_t done_index;
	int cycled;
	int range_whole = 0;
	long nr_to_write = wbc->nr_to_write;

	pagevec_init(&pvec,0);
	if(wbc->range_cyclic){
		writeback_index = mapping->writeback_index;
		index = writeback_index;
		if(index == 0)
			cycled = 1;
		else
			cycled = 0;
		end = -1;
	}else{
		index = wbc->range_start >> PAGE_CACHE_SHIFT;
		end = wbc->range_end >> PAGE_CACHE_SHIFT;
		if(wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
		cycled = 1;
	}
retry:
	done_index = index;
	while (!done && (index <= end)){
		int i;
		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
				PAGECACHE_TAG_DIRTY,
				min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
		if(nr_pages == 0)
			break;
		for(i = 0; i < nr_pages; i++){
			struct page *page = pvec.pages[i];

			if(page->index > end){
				done = 1;
				break;
			}

			done_index = page->index + 1;

			lock_page(page);

			if(unlikely(page->mapping != mapping)){
continue_unlock:
				unlock_page(page);
				continue;
			}
			if(!PageDirty(page)){
				goto continue_unlock;
			}

			if(PageWriteback(page)){
				if(!clear_page_dirty_for_io(page))
					goto continue_unlock;

				ret = (*writepage)(page,wbc,data);
				if(unlikely(ret)){
					if(ret == AOP_WRITEPAGE_ACTIVATE){
						unlock_page(page);
						ret = 0;
					}else{
						done = 1;
						break;
					}
				}
			}

			if(nr_to_write > 0){
				nr_to_write--;
				if(nr_to_write == 0 && wbc->sync_mode == WB_SYNC_NONE){
					done = 1;
					break;
				}
			}
		}
		pagevec_release(&pvec);
		cond_resched();
	}

	if(!cycled && !done){
		cycled = 1;
		index = 0;
		end = writeback_index - 1;
		goto retry;
	}
	if(!wbc->no_nrwrite_index_update){
		if(wbc->range_cyclic || (range_whole && nr_to_write > 0))
			mapping->writeback_index = done_index;
		wbc->nr_to_write = nr_to_write;
	}

	return ret;
}*/



const struct address_space_operations ext2_aops = {
	.readpage		= ext2_readpage,
	.readpages		= ext2_readpages,
	.writepage		= ext2_writepage,
	.sync_page		= block_sync_page,
	.write_begin		= ext2_write_begin,
	.write_end		= generic_write_end,
	.bmap			= ext2_bmap,
	.direct_IO		= ext2_direct_IO,
	.writepages		= ext2_writepages,
	.migratepage		= buffer_migrate_page,
	.is_partially_uptodate	= block_is_partially_uptodate,
	.error_remove_page	= generic_error_remove_page,
};

const struct address_space_operations ext2_aops_xip = {
	.bmap			= ext2_bmap,
	.get_xip_mem		= ext2_get_xip_mem,
};

const struct address_space_operations ext2_nobh_aops = {
	.readpage		= ext2_readpage,
	.readpages		= ext2_readpages,
	.writepage		= ext2_nobh_writepage,
	.sync_page		= block_sync_page,
	.write_begin		= ext2_nobh_write_begin,
	.write_end		= nobh_write_end,
	.bmap			= ext2_bmap,
	.direct_IO		= ext2_direct_IO,
	.writepages		= ext2_writepages,
	.migratepage		= buffer_migrate_page,
	.error_remove_page	= generic_error_remove_page,
};

/*
 * Probably it should be a library function... search for first non-zero word
 * or memcmp with zero_page, whatever is better for particular architecture.
 * Linus?
 */
static inline int all_zeroes(__le32 *p, __le32 *q)
{
	while (p < q)
		if (*p++)
			return 0;
	return 1;
}

/**
 *	ext2_find_shared - find the indirect blocks for partial truncation.
 *	@inode:	  inode in question
 *	@depth:	  depth of the affected branch
 *	@offsets: offsets of pointers in that branch (see ext2_block_to_path)
 *	@chain:	  place to store the pointers to partial indirect blocks
 *	@top:	  place to the (detached) top of branch
 *
 *	This is a helper function used by ext2_truncate().
 *
 *	When we do truncate() we may have to clean the ends of several indirect
 *	blocks but leave the blocks themselves alive. Block is partially
 *	truncated if some data below the new i_size is refered from it (and
 *	it is on the path to the first completely truncated data block, indeed).
 *	We have to free the top of that path along with everything to the right
 *	of the path. Since no allocation past the truncation point is possible
 *	until ext2_truncate() finishes, we may safely do the latter, but top
 *	of branch may require special attention - pageout below the truncation
 *	point might try to populate it.
 *
 *	We atomically detach the top of branch from the tree, store the block
 *	number of its root in *@top, pointers to buffer_heads of partially
 *	truncated blocks - in @chain[].bh and pointers to their last elements
 *	that should not be removed - in @chain[].p. Return value is the pointer
 *	to last filled element of @chain.
 *
 *	The work left to caller to do the actual freeing of subtrees:
 *		a) free the subtree starting from *@top
 *		b) free the subtrees whose roots are stored in
 *			(@chain[i].p+1 .. end of @chain[i].bh->b_data)
 *		c) free the subtrees growing from the inode past the @chain[0].p
 *			(no partially truncated stuff there).
 */

/*
 * here offsets[] stores the offsets of the last block in the file
 * yangsuli
 */
static Indirect *ext2_find_shared(struct inode *inode,
				int depth,
				int offsets[4],
				Indirect chain[4],
				__le32 *top)
{
	Indirect *partial, *p;
	int k, err;

	*top = 0;

	//find where in the depth shoud the branch be truncated
	//after this for loop offsets[k] points to the last suvival block
	//note that if offsets[k-1] = 0, we don't need the block where the offsets[k-1] sits
	//yangsuli
	for (k = depth; k > 1 && !offsets[k-1]; k--)
		;
	partial = ext2_get_branch(inode, k, offsets, chain, &err);
	if (!partial)
		partial = chain + k-1;
	/*
	 * If the branch acquired continuation since we've looked at it -
	 * fine, it should all survive and (new) top doesn't belong to us.
	 */
	write_lock(&EXT2_I(inode)->i_meta_lock);
	if (!partial->key && *partial->p) {
		write_unlock(&EXT2_I(inode)->i_meta_lock);
		goto no_top;
	}
	for (p=partial; p>chain && all_zeroes((__le32*)p->bh->b_data,p->p); p--)
		;
	/*
	 * OK, we've found the last block that must survive. The rest of our
	 * branch should be detached before unlocking. However, if that rest
	 * of branch is all ours and does not grow immediately from the inode
	 * it's easier to cheat and just decrement partial->p.
	 */
	if (p == chain + k - 1 && p > chain) {
	//	p->p--; //YANGSULI: here need change!!!
		p->p -= 2;
	} else {
		*top = *p->p;
		*p->p = 0;
		*(p->p+1) = 0;
	}
	write_unlock(&EXT2_I(inode)->i_meta_lock);

	while(partial > p)
	{
		brelse(partial->bh);
		partial--;
	}
no_top:
	return partial;
}

/**
 *	ext2_free_data - free a list of data blocks
 *	@inode:	inode we are dealing with
 *	@p:	array of block numbers
 *	@q:	points immediately past the end of array
 *
 *	We are freeing all blocks refered from that array (numbers are
 *	stored as little-endian 32-bit) and updating @inode->i_blocks
 *	appropriately.
 */

/* free blocks refered to in an array
 * changed
 * seems like this function is only called by ext2_truncate and ext2_free_branches....
 * and ext2_free_branches is only called by ext2_truncate
 * so may be we can go ahead and change the function signiture....
 * yangsuli
 */
static inline void ext2_free_data(struct inode *inode, __le32 *p, __le32 *q, int ind_block )
{
	unsigned long block_to_free = 0, count = 0;
	unsigned long nr;
	//int step = ind_block == 0 ? 1:2;
	int step = 2;

	for ( ; p < q ; p+=step) {
		nr = le32_to_cpu(*p);
		if (nr) {
			*p = 0;
			*(p+1) = 0; //set the checksum to be 0
			/* accumulate blocks to free if they're contiguous */
			if (count == 0)
				goto free_this;
			else if (block_to_free == nr - count)
				count++;
			else {
				mark_inode_dirty(inode);
				ext2_free_blocks (inode, block_to_free, count);
			free_this:
				block_to_free = nr;
				count = 1;
			}
		}
	}
	if (count > 0) {
		mark_inode_dirty(inode);
		ext2_free_blocks (inode, block_to_free, count);
	}
}

/**
 *	ext2_free_branches - free an array of branches
 *	@inode:	inode we are dealing with
 *	@p:	array of block numbers
 *	@q:	pointer immediately past the end of array
 *	@depth:	depth of the branches to free
 *
 *	We are freeing all blocks refered from these branches (numbers are
 *	stored as little-endian 32-bit) and updating @inode->i_blocks
 *	appropriately.
 */

 /*
  * changed
  * note the the signiture of this function is changed
  * yangsuli
  */
static void ext2_free_branches(struct inode *inode, __le32 *p, __le32 *q, int depth, int ind_block )
{
	struct buffer_head * bh;
	unsigned long nr;
	//int step = ind_block == 0 ? 1:2; //checksum change, yangsuli
	int step = 2;

	if (depth--) {
		int addr_per_block = EXT2_ADDR_PER_BLOCK(inode->i_sb);
		for ( ; p < q ; p+=step) {
			nr = le32_to_cpu(*p);
			if (!nr)
				continue;
			*p = 0;
			*(p+1) = 0;
			bh = sb_bread(inode->i_sb, nr);
			/*
			 * A read failure? Report error and clear slot
			 * (should be rare).
			 */ 
			if (!bh) {
				ext2_error(inode->i_sb, "ext2_free_branches",
					"Read failure, inode=%ld, block=%ld",
					inode->i_ino, nr);
				continue;
			}
			ext2_free_branches(inode,
					   (__le32*)bh->b_data,
					   (__le32*)bh->b_data + addr_per_block,
					   depth,1);
			bforget(bh);
			ext2_free_blocks(inode, nr, 1);
			mark_inode_dirty(inode);
		}
	} else
		ext2_free_data(inode, p, q, ind_block);
}


/*
 * need understood
 * yangsuli
 */
void ext2_truncate(struct inode *inode)
{
	__le32 *i_data = EXT2_I(inode)->i_data;
	struct ext2_inode_info *ei = EXT2_I(inode);
	int addr_per_block = EXT2_ADDR_PER_BLOCK(inode->i_sb);
	int offsets[4];
	Indirect chain[4];
	Indirect *partial;
	__le32 nr = 0;
	int n;
	long iblock;
	unsigned blocksize;

	if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
	    S_ISLNK(inode->i_mode)))
		return;
	if (ext2_inode_is_fast_symlink(inode))
		return;
	if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
		return;

	blocksize = inode->i_sb->s_blocksize;
	//iblock is how many blocks this inode used logically to store its data (only data but not meta data)
	iblock = (inode->i_size + blocksize-1)
					>> EXT2_BLOCK_SIZE_BITS(inode->i_sb);

	if (mapping_is_xip(inode->i_mapping))
		xip_truncate_page(inode->i_mapping, inode->i_size);
	else if (test_opt(inode->i_sb, NOBH))
		nobh_truncate_page(inode->i_mapping,
				inode->i_size, ext2_get_block);
	else
		//this function zeros the segment from i_size to the end of i_mapping
		//Note block_truncate_page also changes the contens of a block (by memset the contents of buffer head!
		block_truncate_page(inode->i_mapping,
				inode->i_size, ext2_get_block);

	n = ext2_block_to_path(inode, iblock, offsets, NULL);
	if (n == 0)
		return;

	/*
	 * From here we block out all ext2_get_block() callers who want to
	 * modify the block allocation tree.
	 */
	mutex_lock(&ei->truncate_mutex);

	if (n == 1) {
		ext2_free_data(inode, i_data+offsets[0]*2,
					i_data + EXT2_NDIR_BLOCKS*2, 0);
		goto do_indirects;
	}

	partial = ext2_find_shared(inode, n, offsets, chain, &nr);
	/* Kill the top of shared branch (already detached) */
	if (nr) {
		if (partial == chain)
			mark_inode_dirty(inode);
		else
			mark_buffer_dirty_inode(partial->bh, inode);
		//the step size doesn't matter since we are just freeing one branch
	       //yangsuli	
		ext2_free_branches(inode, &nr, &nr+1, (chain+n-1) - partial,0);
	}
	/* Clear the ends of indirect blocks on the shared branch */
	while (partial > chain) {
		//here indrect blook freeing
		//yangsuli
		ext2_free_branches(inode,
				   partial->p + 2,
				   (__le32*)partial->bh->b_data+addr_per_block,
				   (chain+n-1) - partial, 1);
		mark_buffer_dirty_inode(partial->bh, inode);
		brelse (partial->bh);
		partial--;
	}
do_indirects:
	/* Kill the remaining (whole) subtrees */
	switch (offsets[0]) {
		default:
			nr = i_data[EXT2_IND_BLOCK*2];
			if (nr) {
				i_data[EXT2_IND_BLOCK*2] = 0;
				i_data[EXT2_IND_BLOCK*2 + 1] = 0; //checksum
				mark_inode_dirty(inode);
				ext2_free_branches(inode, &nr, &nr+1, 1,0);
			}
		case EXT2_IND_BLOCK:
			nr = i_data[EXT2_DIND_BLOCK*2];
			if (nr) {
				i_data[EXT2_DIND_BLOCK*2] = 0;
				i_data[EXT2_DIND_BLOCK*2+1] = 0;
				mark_inode_dirty(inode);
				ext2_free_branches(inode, &nr, &nr+1, 2,0);
			}
		case EXT2_DIND_BLOCK:
			nr = i_data[EXT2_TIND_BLOCK*2];
			if (nr) {
				i_data[EXT2_TIND_BLOCK*2] = 0;
				i_data[EXT2_TIND_BLOCK*2+1] = 0; //checksum
				mark_inode_dirty(inode);
				ext2_free_branches(inode, &nr, &nr+1, 3,0);
			}
		case EXT2_TIND_BLOCK:
			;
	}

	ext2_discard_reservation(inode);

	mutex_unlock(&ei->truncate_mutex);
	inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
	if (inode_needs_sync(inode)) {
		sync_mapping_buffers(inode->i_mapping);
		ext2_sync_inode (inode);
	} else {
		mark_inode_dirty(inode);
	}
}

/* given the inode number and the suber block object, read from disk the 
   ext2_inode object
   yangsuli
 */
static struct ext2_inode *ext2_get_inode(struct super_block *sb, ino_t ino,
					struct buffer_head **p)
{
	struct buffer_head * bh;
	unsigned long block_group;
	unsigned long block;
	unsigned long offset;
	struct ext2_group_desc * gdp;

	*p = NULL;
	if ((ino != EXT2_ROOT_INO && ino < EXT2_FIRST_INO(sb)) ||
	    ino > le32_to_cpu(EXT2_SB(sb)->s_es->s_inodes_count))
		goto Einval;

	block_group = (ino - 1) / EXT2_INODES_PER_GROUP(sb);
	gdp = ext2_get_group_desc(sb, block_group, NULL);
	if (!gdp)
		goto Egdp;
	/*
	 * Figure out the offset within the block group inode table
	 */
	offset = ((ino - 1) % EXT2_INODES_PER_GROUP(sb)) * EXT2_INODE_SIZE(sb);
	block = le32_to_cpu(gdp->bg_inode_table) +
		(offset >> EXT2_BLOCK_SIZE_BITS(sb));
	if (!(bh = sb_bread(sb, block)))
		goto Eio;

	*p = bh;
	offset &= (EXT2_BLOCK_SIZE(sb) - 1);
	return (struct ext2_inode *) (bh->b_data + offset);

Einval:
	ext2_error(sb, "ext2_get_inode", "bad inode number: %lu",
		   (unsigned long) ino);
	return ERR_PTR(-EINVAL);
Eio:
	ext2_error(sb, "ext2_get_inode",
		   "unable to read inode block - inode=%lu, block=%lu",
		   (unsigned long) ino, block);
Egdp:
	return ERR_PTR(-EIO);
}

/* cope ext2_inode flages into general inode->flags
 * yangsuli
 */
void ext2_set_inode_flags(struct inode *inode)
{
	unsigned int flags = EXT2_I(inode)->i_flags;

	inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
	if (flags & EXT2_SYNC_FL)
		inode->i_flags |= S_SYNC;
	if (flags & EXT2_APPEND_FL)
		inode->i_flags |= S_APPEND;
	if (flags & EXT2_IMMUTABLE_FL)
		inode->i_flags |= S_IMMUTABLE;
	if (flags & EXT2_NOATIME_FL)
		inode->i_flags |= S_NOATIME;
	if (flags & EXT2_DIRSYNC_FL)
		inode->i_flags |= S_DIRSYNC;
}

/* Propagate flags from i_flags to EXT2_I(inode)->i_flags */
/*
 *  understood
 * yangsuli
 */
void ext2_get_inode_flags(struct ext2_inode_info *ei)
{
	unsigned int flags = ei->vfs_inode.i_flags;

	ei->i_flags &= ~(EXT2_SYNC_FL|EXT2_APPEND_FL|
			EXT2_IMMUTABLE_FL|EXT2_NOATIME_FL|EXT2_DIRSYNC_FL);
	if (flags & S_SYNC)
		ei->i_flags |= EXT2_SYNC_FL;
	if (flags & S_APPEND)
		ei->i_flags |= EXT2_APPEND_FL;
	if (flags & S_IMMUTABLE)
		ei->i_flags |= EXT2_IMMUTABLE_FL;
	if (flags & S_NOATIME)
		ei->i_flags |= EXT2_NOATIME_FL;
	if (flags & S_DIRSYNC)
		ei->i_flags |= EXT2_DIRSYNC_FL;
}

/*
 * read from disk the raw inode then fill the inode object in memory
 * changed
 * yangsuli
 */
struct inode *ext2_iget (struct super_block *sb, unsigned long ino)
{
	struct ext2_inode_info *ei;
	struct buffer_head * bh;
	struct ext2_inode *raw_inode;
	struct inode *inode;
	long ret = -EIO;
	int n;

	/*
	 * search it in the inode cache
	 * if found, return it
	 * if not, allocate a new inode and return this empty one
	 */
	inode = iget_locked(sb, ino);

	if (!inode)
		return ERR_PTR(-ENOMEM);

	// if this is found in inode  cache
	if (!(inode->i_state & I_NEW))
		return inode;

	ei = EXT2_I(inode);
	ei->i_block_alloc_info = NULL;

	raw_inode = ext2_get_inode(inode->i_sb, ino, &bh);
	if (IS_ERR(raw_inode)) {
		ret = PTR_ERR(raw_inode);
 		goto bad_inode;
	}

	inode->i_mode = le16_to_cpu(raw_inode->i_mode);
	inode->i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
	inode->i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
	if (!(test_opt (inode->i_sb, NO_UID32))) {
		inode->i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
		inode->i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
	}
	inode->i_nlink = le16_to_cpu(raw_inode->i_links_count);
	inode->i_size = le32_to_cpu(raw_inode->i_size);
	inode->i_atime.tv_sec = (signed)le32_to_cpu(raw_inode->i_atime);
	inode->i_ctime.tv_sec = (signed)le32_to_cpu(raw_inode->i_ctime);
	inode->i_mtime.tv_sec = (signed)le32_to_cpu(raw_inode->i_mtime);
	inode->i_atime.tv_nsec = inode->i_mtime.tv_nsec = inode->i_ctime.tv_nsec = 0;
	ei->i_dtime = le32_to_cpu(raw_inode->i_dtime);
	/* We now have enough fields to check if the inode was active or not.
	 * This is needed because nfsd might try to access dead inodes
	 * the test is that same one that e2fsck uses
	 * NeilBrown 1999oct15
	 */
	if (inode->i_nlink == 0 && (inode->i_mode == 0 || ei->i_dtime)) {
		/* this inode is deleted */
		brelse (bh);
		ret = -ESTALE;
		goto bad_inode;
	}
	inode->i_blocks = le32_to_cpu(raw_inode->i_blocks);
	ei->i_flags = le32_to_cpu(raw_inode->i_flags);
	ei->i_faddr = le32_to_cpu(raw_inode->i_faddr);
	ei->i_frag_no = raw_inode->i_frag;
	ei->i_frag_size = raw_inode->i_fsize;
	ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl);
	ei->i_dir_acl = 0;
	if (S_ISREG(inode->i_mode))
		inode->i_size |= ((__u64)le32_to_cpu(raw_inode->i_size_high)) << 32;
	else
		ei->i_dir_acl = le32_to_cpu(raw_inode->i_dir_acl);
	ei->i_dtime = 0;
	inode->i_generation = le32_to_cpu(raw_inode->i_generation);
	ei->i_state = 0;
	ei->i_block_group = (ino - 1) / EXT2_INODES_PER_GROUP(inode->i_sb);
	ei->i_dir_start_lookup = 0;

	/*
	 * NOTE! The in-memory inode i_data array is in little-endian order
	 * even on big-endian machines: we do NOT byteswap the block numbers!
	 */
	for (n = 0; n < EXT2_N_BLOCKS ; n++){//checksum yangsuli
		ei->i_data[n*2] = raw_inode->i_block[n*2];
		ei->i_data[n*2+1] = raw_inode->i_block[n*2+1];
	}


	if (S_ISREG(inode->i_mode)) {
		inode->i_op = &ext2_file_inode_operations;
		if (ext2_use_xip(inode->i_sb)) {
			inode->i_mapping->a_ops = &ext2_aops_xip;
			inode->i_fop = &ext2_xip_file_operations;
		} else if (test_opt(inode->i_sb, NOBH)) {
			inode->i_mapping->a_ops = &ext2_nobh_aops;
			inode->i_fop = &ext2_file_operations;
		} else {
			inode->i_mapping->a_ops = &ext2_aops;
			inode->i_fop = &ext2_file_operations;
		}
	} else if (S_ISDIR(inode->i_mode)) {
		inode->i_op = &ext2_dir_inode_operations;
		inode->i_fop = &ext2_dir_operations;
		if (test_opt(inode->i_sb, NOBH))
			inode->i_mapping->a_ops = &ext2_nobh_aops;
		else
			inode->i_mapping->a_ops = &ext2_aops;
	} else if (S_ISLNK(inode->i_mode)) {
		if (ext2_inode_is_fast_symlink(inode)) {
			inode->i_op = &ext2_fast_symlink_inode_operations;
			nd_terminate_link(ei->i_data, inode->i_size,
				sizeof(ei->i_data) - 1);
		} else {
			inode->i_op = &ext2_symlink_inode_operations;
			if (test_opt(inode->i_sb, NOBH))
				inode->i_mapping->a_ops = &ext2_nobh_aops;
			else
				inode->i_mapping->a_ops = &ext2_aops;
		}
	} else {
		inode->i_op = &ext2_special_inode_operations;
		if (raw_inode->i_block[0])
			init_special_inode(inode, inode->i_mode,
			   old_decode_dev(le32_to_cpu(raw_inode->i_block[0])));
		else 
			init_special_inode(inode, inode->i_mode,
			   new_decode_dev(le32_to_cpu(raw_inode->i_block[1])));
	}
	brelse (bh);
	ext2_set_inode_flags(inode);
	unlock_new_inode(inode);
	return inode;
	
bad_inode:
	iget_failed(inode);
	return ERR_PTR(ret);
}

/* 
 * given an in-memory inode, wirte it to disk
 * changed
 * yangsuli
 */
int ext2_write_inode(struct inode *inode, int do_sync)
{
	struct ext2_inode_info *ei = EXT2_I(inode);
	struct super_block *sb = inode->i_sb;
	ino_t ino = inode->i_ino;
	uid_t uid = inode->i_uid;
	gid_t gid = inode->i_gid;
	struct buffer_head * bh;
	struct ext2_inode * raw_inode = ext2_get_inode(sb, ino, &bh);
	int n;
	int err = 0;

	if (IS_ERR(raw_inode))
 		return -EIO;

	/* For fields not not tracking in the in-memory inode,
	 * initialise them to zero for new inodes. */
	if (ei->i_state & EXT2_STATE_NEW)
		memset(raw_inode, 0, EXT2_SB(sb)->s_inode_size);

	ext2_get_inode_flags(ei);
	raw_inode->i_mode = cpu_to_le16(inode->i_mode);
	if (!(test_opt(sb, NO_UID32))) {
		raw_inode->i_uid_low = cpu_to_le16(low_16_bits(uid));
		raw_inode->i_gid_low = cpu_to_le16(low_16_bits(gid));
/*
 * Fix up interoperability with old kernels. Otherwise, old inodes get
 * re-used with the upper 16 bits of the uid/gid intact
 */
		if (!ei->i_dtime) {
			raw_inode->i_uid_high = cpu_to_le16(high_16_bits(uid));
			raw_inode->i_gid_high = cpu_to_le16(high_16_bits(gid));
		} else {
			raw_inode->i_uid_high = 0;
			raw_inode->i_gid_high = 0;
		}
	} else {
		raw_inode->i_uid_low = cpu_to_le16(fs_high2lowuid(uid));
		raw_inode->i_gid_low = cpu_to_le16(fs_high2lowgid(gid));
		raw_inode->i_uid_high = 0;
		raw_inode->i_gid_high = 0;
	}
	raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);
	raw_inode->i_size = cpu_to_le32(inode->i_size);
	raw_inode->i_atime = cpu_to_le32(inode->i_atime.tv_sec);
	raw_inode->i_ctime = cpu_to_le32(inode->i_ctime.tv_sec);
	raw_inode->i_mtime = cpu_to_le32(inode->i_mtime.tv_sec);

	raw_inode->i_blocks = cpu_to_le32(inode->i_blocks);
	raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
	raw_inode->i_flags = cpu_to_le32(ei->i_flags);
	raw_inode->i_faddr = cpu_to_le32(ei->i_faddr);
	raw_inode->i_frag = ei->i_frag_no;
	raw_inode->i_fsize = ei->i_frag_size;
	raw_inode->i_file_acl = cpu_to_le32(ei->i_file_acl);
	if (!S_ISREG(inode->i_mode))
		raw_inode->i_dir_acl = cpu_to_le32(ei->i_dir_acl);
	else {
		raw_inode->i_size_high = cpu_to_le32(inode->i_size >> 32);
		if (inode->i_size > 0x7fffffffULL) {
			if (!EXT2_HAS_RO_COMPAT_FEATURE(sb,
					EXT2_FEATURE_RO_COMPAT_LARGE_FILE) ||
			    EXT2_SB(sb)->s_es->s_rev_level ==
					cpu_to_le32(EXT2_GOOD_OLD_REV)) {
			       /* If this is the first large file
				* created, add a flag to the superblock.
				*/
				lock_kernel();
				ext2_update_dynamic_rev(sb);
				EXT2_SET_RO_COMPAT_FEATURE(sb,
					EXT2_FEATURE_RO_COMPAT_LARGE_FILE);
				unlock_kernel();
				ext2_write_super(sb);
			}
		}
	}
	
	raw_inode->i_generation = cpu_to_le32(inode->i_generation);
	/*here if its char or block device, i_blocks remain the same without checksum
	  *yangsuli
	  */
	if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
		if (old_valid_dev(inode->i_rdev)) {
			raw_inode->i_block[0] =
				cpu_to_le32(old_encode_dev(inode->i_rdev));
			raw_inode->i_block[1] = 0;
		} else {
			raw_inode->i_block[0] = 0;
			raw_inode->i_block[1] =
				cpu_to_le32(new_encode_dev(inode->i_rdev));
			raw_inode->i_block[2] = 0;
		}
	} else for (n = 0; n < EXT2_N_BLOCKS; n++){
		raw_inode->i_block[n*2] = ei->i_data[n*2];
		raw_inode->i_block[n*2+1] = ei->i_data[n*2+1];
		//wrtie the checksum, yangsuli
	}
	mark_buffer_dirty(bh);
	if (do_sync) {
		sync_dirty_buffer(bh);
		if (buffer_req(bh) && !buffer_uptodate(bh)) {
			printk ("IO error syncing ext2 inode [%s:%08lx]\n",
				sb->s_id, (unsigned long) ino);
			err = -EIO;
		}
	}
	ei->i_state &= ~EXT2_STATE_NEW;
	brelse (bh);
	return err;
}

int ext2_sync_inode(struct inode *inode)
{
	struct writeback_control wbc = {
		.sync_mode = WB_SYNC_ALL,
		.nr_to_write = 0,	/* sys_fsync did this */
	};
	return sync_inode(inode, &wbc);
}

int ext2_setattr(struct dentry *dentry, struct iattr *iattr)
{
	struct inode *inode = dentry->d_inode;
	int error;

	error = inode_change_ok(inode, iattr);
	if (error)
		return error;
	if ((iattr->ia_valid & ATTR_UID && iattr->ia_uid != inode->i_uid) ||
	    (iattr->ia_valid & ATTR_GID && iattr->ia_gid != inode->i_gid)) {
		error = vfs_dq_transfer(inode, iattr) ? -EDQUOT : 0;
		if (error)
			return error;
	}
	error = inode_setattr(inode, iattr);
	if (!error && (iattr->ia_valid & ATTR_MODE))
		error = ext2_acl_chmod(inode);
	return error;
}
